1. Field of Invention
The present invention relates to a region based shutter adaptation method for image exposure; particularly, it relates to such a method capable of exposing different regions within an image which is non-uniformly illuminated by different exposure parameters to better extract information in such a non-uniformly illuminated image.
2. Description of Related Art
Referring to FIG. 1, conventionally, a prior art shutter control method assumes that an image 10 is uniformly illuminated across the whole image, and hence the shutter exposes the image 10 by one exposure region SR1 which covers the whole image 10, and the exposure parameters such as time duration of exposure (exposure duration) are the same for every pixel in the image 10.
However, if an image does not comply with the assumption, i.e., the image is not uniformly illuminated, which is often the case when the image is taken under low natural light, the conventional method can not obtain complete and sufficient information of the image.
Referring to FIGS. 2A and 2B, which show an image 20 which is non-uniformly illuminated but is exposed by the same exposure duration (e.g., 100 ms) across the whole image. As shown in FIGS. 2A and 2B, the shutter is adapted to the brightest region R1 in the image, i.e., the exposure duration is determined by taking the brightest region R1 as the priority concern. Therefore, all other parts of the image 20 is underexposed. For example, the region R2 which is the darkest region in the image 20 is underexposed. Any information or feature that is contained in this region R2 is lost and can not be extracted.
In summary, the conventional shutter control method exposes an image by one exposure region with the same exposure parameters across the whole image. If the image is not uniformly illuminated such that the brightness conditions vary greatly in the image, the conventional shutter control method can only adapt the shutter to a small brightness range within the image, and the information or feature that is contained in the other part of the image is lost. For example, if the shutter is adapted to the brightest region, the information or feature that is contained in a darker part of the image is lost; if the shutter is adapted to the darkest region, the information or feature that is contained in a brighter part of the image is lost.
In view of the above, to overcome the drawback in the prior art, the present invention proposes a shutter adaptation method capable of exposing different regions of an image by different exposure parameters to better extract information in a non-uniformly illuminated image.